Australian search officials have halved the smaller part of the search zone for the missing Malaysia Airlines flight dedicated to sonobuoy detections in what may be the last days that black box signals can be detected.

The search zone for the missing plane, which is believed to have crashed in the Indian Ocean claiming the lives of all passengers on board, now totals approximately 57,506 sq km. But a smaller search area using sonobuoys to detect signals from the black boxes of the plane has halved in the last 48 from 600 sq km to just 340 sq km on Sunday.

Black box pulses can usually last around 30 days, and the search has now been going for closer to 40. Search officials are still holding out that they may pick up further signals, following four earlier detections last week on two separate occasions by the Australian defence vessel Ocean Shield.

A fifth signal was also detected later in the week, but on further analysis was determined not to be a black box pulse.

The head of Australia’s joint coordinate centre Angus Houston also said during the week he was confident search officials were looking in the right place.

“I believe we are searching in the right area but we need to identity wreckage to be sure that this is the final resting place of MH370,” he said.

As the black boxes batteries fade the searchers may be forced to deploy a remote underwater vehicle to begin visually scanning the ocean floor - a process that will be far more time consuming than the searches that the Ocean Shield are currently capable of undertaking with their equipment.

There are currently up to 11 military aircraft, one civil aircraft and 14 ships assist in the search on Sunday.